Foam insulated tank

ABSTRACT

A method of manufacturing a foam insulated water heater of the type having an inner tank, a layer of insulating foam material surrounding the inner tank and an outer protective shell includes, in one embodiment, the steps of (1) forming a flexible, expandable bag in a configuration which may be placed between the tank and shell, (2) attaching the flexible bag between the tank and shell, (3) filling the bag with a foam material which expands, and (4) continuing to fill the bag so that foam material expands through relief openings in the bag to fill the remainder of the space between the tank and the shell.

This application is a division of application Ser. No. 705,226, filedFeb. 25, 1985, now U.S. Pat. No. 4,632,792.

The prior application is assigned of record to Rheem ManufacturingCompany.

BACKGROUND OF THE INVENTION

This invention relates to an improved method for the manufacture ofinsulated containers, particularly water heaters.

Electric and gas water heaters are generally comprised of a glass-lined,metal tank usually in the form of a cylinder which is surrounded by aninsulating material retained about the tank by means of a protective,outer, sheet metal shell. In gas models, a burner compartment isnormally located below the tank within the protective sheet metal shell.In electric models, a heating element normally projects through a sidewall of the tank.

In order to improve the efficiency of such water heaters, it isdesirable to provide external insulation for the tanks between the tankand the outer shell. Heretofore Fiberglas insulation has proven to be anexcellent insulating material. More recently, expanded urethane foam hasbeen utilized as the insulating material surrounding a water heatertank.

One of the problems associated with such a water heater assembly,particularly one having urethane foam as the insulating material, hasbeen the method by which the foam material is formed about the tank.Generally the foam is injected as a liquid into the annular spacebetween the inner tank and outer shell. However, it is necessary to usea core piece or other mold forming device within the space between theinner tank and outer protective shell to retain the foam within adesired region. For example, in an electric model the heating rod andcontrols are attached to the side wall of the tank and cannot be coveredwith foam.

One way of preventing foam from covering or forming over the controlshas been to pack the region around the controls with Fiberglasinsulation material. The Fiberglas insulation material then serves as abarrier during the foam molding operation.

Another procedure has been adopted by State Industries, Inc. of AshlandCity, Tenn. The State Industries procedure calls for forming a flexibleplastic bag with an open top, closed sides and a closed bottom edge. Thebag then attaches to and partially encircles the inner tank. Expandableurethane foam is next injected into the bag causing the bag to expandand fill the space between the inner tank and the outer shell of theheater. In practice, the bag extends only partially around thecircumference of the tank thus leaving a space or void in the regionbetween the inner tank and outer shell defined by the opposite ends ofthe bag. Controls, inlets, outlets and the like are positioned in thevoid region, and the spaces between the controls are appropriatelypacked with a Fiberglas insulation material.

Another procedure is described in U.S. Pat. No. 4,372,028 issued Feb. 8,1983 for a Method of Manufacturing Foam Insulated Tank. In that patent,the use of a small flexible bag to define the control space and theboundary for flow of foam material is disclosed. That invention permitsutilization of expandable foam over substantially the entire outsidesurface area of a water heater tank. The method insures accurate andeasily reproducible positioning of voids or spaces in the insulationthrough which controls, inlets, outlets and the like may be affixed tothe tank. The method also eliminates usage of a large plastic bag fromthe manufacturing process and substitutes usage of a smaller, lessexpensive bag. As a result, undesired folds which may form in the largebag are avoided. Also, the insulating capability of the foam is enhancedsince the foam will bond directly to the walls of the container and willnot be retained in an air permeable bag. U.S. Pat. No. 4,372,028 isincorporated herewith by reference.

The present invention is an improvement of the subject matter of U.S.Pat. No. 4,372,028 and is especially useful in the manufacture ofelectric water heaters. The present invention eliminates the need for asecondary, separate injection of foam material as described in U.S. Pat.No. 4,372,028. Additionally, there is less leakage of foam material aswell as less possibility for distortion of the flexible bag during themanufacturing process.

Thus, it is an object of the invention to provide an improved method ofmanufacturing a multiple layer container of the type having an innerwall, an intermediate insulating layer and an outer protective wall.

A further object of the present invention is to provide a method ofmanufacturing a water heater tank having an inner metal tank, anintermediate layer of expanded urethane foam material and an outerprotective shell or cover.

Still another object of the present invention is to provide a method ofmanufacturing a multiple layer container having improved insulatingfeatures, improved economy of manufacture, and which does not requiresignificant capital investment in new equipment.

Another object of the invention is to eliminate the necessity of using alarge, tank encompassing bag to receive foam and surround an inner metaltank in an assembly which incorporates an inner tank, an insulatinglayer on the tank and an outer shell over the insulating layer.

A further object of the invention is to provide a method ofmanufacturing a foam insulating tank assembly having a single foaminjection step.

These and other objects advantages and features of the invention will beset forth in the detailed description which follows.

SUMMARY OF THE INVENTION

Briefly, the present invention comprises a method of manufacturing amultiple layer container of the type having an inner wall, anintermediate layer of expanded foam material and an outer wall. Theinner and outer walls serve to retain the expanded foam material duringthe manufacturing process. The method comprises the steps of (1) forminga flexible, expandable bag in a configuration which may be attached tothe inner wall, (2) positioning the flexible bag in the desired positionon the inner wall, (3) positioning the outer wall in spaced relation andabout the flexible bag and inner wall to define a space between theinner wall and outer wall, (4) filling the flexible bag, which hasrelief openings, with expandable foam material; and (5) expanding theflexible bag contents to form a barrier between the inner and outerwalls while filling the remaining space between the walls withexpandable foam flowing through relief openings in the bag. The sequenceof the aforesaid steps may be altered. The configuration of the flexiblebag and the position and manner of attachment to the tank may also bevaried to define different sections of the mold wall. The flexible bagis configured to define voids or spaces in the final foam layer of themultiple layer container.

BRIEF DESCRIPTION OF THE DRAWING

In the detailed description which follows, reference will be made to thedrawing comprised of the following figures:

FIG. 1, parts A through D, is a schematic representation of thesequential steps of an embodiment of the manufacturing process of thepresent invention;

FIG. 2 is a perspective view of the preferred embodiment of the flexiblebag used in the process; and

FIG. 3 is an enlarged perspective view of the flexible bag of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the figures, FIG. 1, parts A-D relate, in general, to the method ofmanufacture of an electric water heater utilizing the method of thepresent invention. It is, of course, possible to utilize the techniquesand method of the present invention for manufacture of other devices inaddition to water heaters. The invention thus relates to the method ofmanufacture of any multi-layered container wherein the intermediatelayer is comprised of expanded foam, for example expanded urethane foam,and the other or surrounding layers are comprised of walls which act asa mold form, at least in part, for the expanded foam material. Thus,inner and the outer walls serve only as mold forms in forming theopposite side faces of the insulating layer. The invention relatesparticularly to the method for forming voids or passages through theinsulating layer between the walls for receipt of controls, inlets andoutlets, etc.

In general, a flexible bag, for example a polyethylene bag, which issized and configured to fit in the space between the inner and outerwalls, is provided with one or more sealed passages therethrough. Thebag expands tightly against the inner and outer walls when filled withexpandable foam material. Thus, the bag is positioned between the innerand outer walls, filled with foam and permitted to expand tightlyagainst the inner and outer walls. The flexible and expandable bag canbe configured so that voids or spaces will be defined by the bag betweenthe walls. Importantly, in addition, the bag includes at least onerelief opening through the bag to the region between the inner wall andouter wall for the flow of foam material from the bag into the spacebetween the inner wall and outer wall or shell. Thus, it is possible tosimply inject foam material into the flexible bag to fill the bag aswell as the entire space between the walls. The provision of reliefopenings in the bag as well as diversion panels within the bagassociated with the relief openings insures sequential filling of thebag by foam material followed by filling the space between the walls.Further details of these features are set forth with respect to thespecific example of the invention discussed below.

METHOD OF MANUFACTURING ELECTRIC WATER HEATER

FIG. 1, parts A-D, illustrates application of the method of the presentinvention to the manufacture of a typical electric water heater tankassembly. As shown in FIG. 1A, a tank 32 is generally cylindrical inshape and has a closed top and bottom. A control panel 34 is defined onthe side of the tank 32 projecting from surface 33. Panel 34 maycomprise, for example, controls mounted on the wall surface 33 of thetank and projecting outward, as well as electric heating rod elementswhich project into the interior of the tank 32.

An expandable flexible bag 36, preferably of a polyethylene plasticmaterial, is formed to receive expandable foam, for example, urethanefoam. As shown in FIG. 2, bag 36 is formed as a tube by opposed flatsheets of plastic material which are heat sealed together along sealededges 40, 42 and 44 to form the bag 36 with a top opening 38. A void oropening 46 is defined in the bag 36 by overlying cutouts in the sheetswhich are sealed along a circular or oblong sealed edge 48. In otherwords, the sheets of polyethylene or plastic material forming the bag 36are sealed along the edge 48 to define opening 46. An optional supportflap 50 is defined adjacent the top opening 38.

As depicted in FIGS. 2 and 3, the bag 36 includes, in the embodimentshown, a series of six relief passages or openings 70, 72, 74, 76, 78,80 in the side walls of bag 36. The relief passages 70, 72, 74, 76, 78,80 are divided into opposite sets of three passages 70, 72, 74 and 76,78, 80. Each set of passages 70, 72, 74 and 76, 78, 80 are positioned onopposite sides of bag 36, the lowest being generally above the initialliquid level of the injected foam material and preferably verticallyabove the void or opening 46 through bag 36. In this manner, when foammaterial is injected into bag 36, foam material will initially fill thebottom of bag 36, and expand in the region adjacent void 46 beforespilling through passages 70, 72, 74, 76, 78, 80. As a result, the bag36 will be held substantially rigid in position between tank 32 and anouter shell or wall 52 before foam material flows from bag 36. Also, thepassages 70, 72, 74, 76, 78, 80 are preferably aligned and oriented sothat they lead directly into the annular space between tank 32 and shell52.

As depicted in FIG. 2, the bag 36 may include diversion shunts 71, 73,75, 77, 79 and 81 associated with each or some of the relief openings70, 72, 74, 76, 78 and 80, respectively. Diversion shunt 71 is exemplaryof the structure and function of the diversion shunts. Shunt 71 isformed by heat sealing a sector of the bag 36, which is polyethylene orother bag material. The shunt 71 may thus be formed by sealing the sidesof bag 36 together above opening 70 along a line which inclines downwardfrom above opening 70 for a distance approximately equal to the diameterof opening 70. The downward inclination of shunt 71 is preferably 30° to45° from horizontal though this angle may be varied to accommodate thefoam material being used for example.

In review, the shunt 71 preferably has a straight line form when the bag36 is filled. The shunt 71 is also preferably inclined slightly downwardwith respect to a vertical central axis 82 of the bag 36. In thismanner, as the bag 36 is filled with foam material, the bag 36 willinitially fill at the bottom. As the level of foam material increasesdue to the addition of foam material and the expansion thereof, foammaterial will be diverted, in part, by the shunt 71 through theassociated opening or passage 70. By positioning the opening 70 as wellas the shunt 71 above the void 46, the lower portion of the bag 36 willexpand and hold the bag in position. Then as the bag 36 fills, foammaterial will exude through the passages, as at 70, being diverted, inpart, by the shunt 71. FIG. 3 is an enlarged cutaway section of the bag36 illustrating the manner in which the shunt 71 is positioned relativeto the passage 70 and also relative to vertical axis 82 associated withthe bag 36 as the bag 36 is positioned on the outside surface 33 of tank32.

As shown in FIG. 1B, the bag 36 is initially affixed to the side of thetank 32. For example, the optional flap 50 may be taped to the top oftank 32 in order to support the bag 36 on the outside surface 33 of thetank 32. The bag 36 is dimensioned to extend from the top to the bottomof the tank 32. Also, the void or opening 46 is positioned over thepanel 34. Optionally, the bag 36 may be attached to the surface 33 oftank 32 or to the inner surface of the outer shell 52 by use of hot meltglue or another adhesive, for example.

FIG. 1C illustrates the next step in the manufacture of the assembly.First, outer shell 52 is positioned over the tank 32 and bag 36.Optionally, of course, if the bag 36 is attached to shell 52, both fitover tank 32. Note that in an electric water heater, the shell 52 hasapproximately the same elevational dimension as the tank 32. Thisresults because there is no requirement for a burner section below thetank 32. The shell 52 also includes an access port 56 which is placed inregister with opening 46 and panel 34.

As depicted by FIG. 1D, subsequent to positioning the shell 52 withrespect to the tank 32, an expandable foam material is injected into thebag 36 by means of injector mechanism 54. The foam material is thenpermitted to expand. In this manner the bag 36 impinges on the opposedsurfaces of the tank 32 and shell 52 simultaneously along a narrowlongitudinal strip defined by bag 36. The opening 46 is maintained inproper register with the panel 34 on the tank 32 and an opening 56defined in the outer shell 52. Consequently, proper access can bemaintained for inserting a heating element or other controls into thetank 32. Though only one bag 36 having a single opening 46 is described,it is possible to have multiple bags having any number of openings orwithout openings.

As also represented by FIG. 1D, the outer shell 52 connects to a lowerend or bottom panel 58 that blocks foam material. This lower end 58 thusdefines the bottom of a mold form which is adapted to receive expandablefoam. A top cover of pan 59 fits over the top of shell 52 and includesan opening 61 for receipt of a foam injector mechanism 54.Alternatively, the foam material may be injected before positioning pan59 on the shell 52.

As shown in FIG. 1D, the injector mechanism 54 is used to inject foammaterial into the annular space between the shell 52 and tank 32 byintroduction through bag 36 and subsequent flow through relief openings70, 72, 74, 76, 78, 80 as required. This foam will flow into bag 36 andthen flows from bag 36, through the relief openings, e.g. 70 as divertedby shunt 71, and about the tank 32. The foam will subsequently expand toform an insulating layer 60 partially depicted in FIG. 1D which totallysurrounds the tank 32.

It can be seen that the application of the method of the presentinvention illustrated in FIG. 1 contemplates utilization of a flexibleexpandable bag to define, in part the mold form in the space between acontainer or tank and an outer shell. Many variations of the describedmethod are possible. Container size and shape may vary. Expandable bagsize and position may vary. The number, size and position of reliefpassages or openings in the bag may vary. The shape, size and positionof shunts in the bag may be varied. Thus, while there has been set fortha preferred embodiment of the invention, it is to be understood that theinvention is to be limited only by the following claims and theirequivalents.

What is claimed is:
 1. An improved water tank assembly comprising, incombination:(a) an inner tank for containing water defining a verticalaxis; (b) an outer shell surrounding the inner tank and spaced from theinner tank, said outer shell including at least one opening for accessto the inner tank; (c) a bottom pan between the inner tank and outerwall; (d) a flexible bag having a void therethrough defining a passagealigned with the outer shell opening, said bag including at least .[.oneside relief opening into.]. .Iadd.a plurality of vertically displacedrelief openings in a vertical portion of the side of the bag openinginto .Iaddend.the space between the inner tank and outer shell and alsoincluding a top opening, said bag being generally elongated and alignedwith the vertical axis; .[.and.]. (e) said bag being filled withexpandable foam material through the top opening to fill the bag andthen the space between the inner tank and outer shell by flow throughthe relief .[.opening..]. .Iadd.openings, first through the lower ofsaid vertically displaced relief openings and then through the upper ofsaid vertically displaced relief openings; (f) said bag further having adiversion shunt formed in the bag above each relief opening fordiverting some of the expandable foam through the associated reliefopening. .Iaddend. .[.2. The assembly of claim 1 including diversionmeans within the bag for directing flow of expandable foam..]. .[.3. Theassembly of claim 1 wherein the bag includes a plurality of reliefopenings..].
 4. The assembly of claim 1 wherein .[.the bag includes aplurality of.]. .Iadd.said .Iaddend.relief openings .Iadd.are.Iaddend.arranged vertically one above the other on opposite sides ofthe bag for discharge of foam material into the space.
 5. The assemblyof claim 1 .[.including a.]. .Iadd.wherein each said .Iaddend.diversionshunt .Iadd.is .Iaddend.defined by a flexible, generally short linearseal of the bag extending laterally from the edge of the bag slightlyinclined down towards the center of the bag and positioned verticallyabove a relief opening for diverting some foam material from the bagwhile simultaneously permitting some flow of foam material into thelength of the bag.